there are living creatures in the outer space as those on Earth hasn’t been proved so far

问题补充：

there are living creatures in the outer space as those on Earth hasn’t been proved so far.

A. When

B. How

C. If

D. Whether

答案：

A. When

B. How

C. If

(答案→)D. Whether

解析：考查主语从句：句意：外层空间是否和地球上一样有生物到现在还没有证实。AB项when，How不符合句意，C项if不能引导主语从句。选D。